MBED is a microcontroller that was designed for quick prototyping. As you see in the video, Steve, one of the beta testers of the mbed managed to hack a billy bass.

If you click through, you'll find a variation on this experiment where Steve managed to get the Billy Bass to read out twitter mentions for its twitter account via a webserver and an ethernet connection (no computer!).

There's already some resources being shared and you can program it using C++. The other cool thing is that it's just $60 if you preorder. I own one of these Billy Bass things and I'd love to hack around with it over Christmas break.